The relationships between the serum levels of estradiol, progesterone, and prolactin have been analyzed in normal women in relation to age, menstrual cycle, and in oral contraceptive (OC) users. We have been able to detect signficant differences between the prolactinemia values during the cycle in different age groups as well as following OCs. A word of caution is presented for the evaluation of the prolactin blood level which should be always related to the physiological phase of the cycle and to the age of the subjects. (author's)